1. Field of the Invention
The invention relates generally to devices and methods that are useful for measuring the thermal expansion and/or chemical reactivity of aggregates used in concrete and like substances.
2. Description of the Related Art
Techniques for determining the coefficient of thermal expansion, and related expansion information, for a particular aggregate type are important, as such properties determine the thermal expansion of concrete using that aggregate type to a considerable degree. Techniques for determining the chemical reactivity of aggregate types are important for similar reasons. Chemically reactive aggregates can expand greatly over time inside a concrete mixture, which may lead to cracking thereby weakening the structure of the concrete.
To date, techniques for determining information concerning the expansion of aggregates and substances containing aggregates have generally involved the use of flasks to contain crushed pieces of aggregate mixed with water. To measure aggregate expansion, these arrangements also relied upon a readings of the levels of a delicate balance of water and mercury contained in a complex arrangements of tubes and stopcocks. These prior art techniques were also relatively limited, of questionable accuracy and incapable of measurements over wide temperatures.
Further, such techniques (which were limited to thermal expansion testing) provided no reliable means of determining the actual temperature of the aggregate being tested. Instead, it was assumed that the aggregate samples were at the same temperature as the water bath surrounding the flask.
Other methods of determining information relating to the expansion of aggregate utilized direct measurement of individual aggregates by placing chunk aggregate members inside a clamp or similar retainer and gauging how much the individual member expands as temperature is changed. Unfortunately, information obtained from this type of measurement is not accurately generalized to larger amounts of aggregates.
Existing alkali silica reaction (ASR) techniques for testing the chemical reactivity of aggregates also have significant limitations. These tests do not always provide reliable results or results that maybe applicable to the prediction of performance under similar conditions in the field.
The invention addresses the problems of the prior art.
The invention provides methods and devices for improved measurement of the thermal expansion and/or chemical reactivity of aggregates used in concrete and for similar substances. In a preferred embodiment, aggregate is placed into the chamber of a metallic container having an enlarged opening. The aggregate is placed in a water bath, and a tightly sealable lid is placed onto the container. The lid carries a linear variable differential transducer (LVDT). A thermocouple for sensing temperature is also retained within the lid so that a sensor on the thermocouple contacts the water bath when the lid is secured onto the container. The LVDT is operationally interconnected with a storage or recording device. In a preferred construction the lid retains a tower member having a float that is freely moveably mounted upon a guide rod. Movement of the float is indicative of a volumetric change in the aggregate and water.
In operation, the dilatometer device is used to determine the information relating to the amount of expansion or contraction of the aggregate in response to thermal changes. In addition, the devices and methods of the present invention are useful for determining the degree of reactivity of the aggregate. Preferably, he dilatometer is calibrated before use with aggregate by filling the container with water alone and then determining the thermal expansion associated with the water in the particular container being used. The degree of volumetric change for the aggregate alone may be determined using equations that isolate and remove the expansion quotient of the water.